Block level space time transmit diversity in wireless communications

ABSTRACT

Space time transmit diversity ( 9, 14, 17, 19 ) is applied at the block level to an original block of bits ( 12 ) in order to reduce the effects of fading in wireless communication systems that use nonlinear modulation schemes ( 13, 33 ). At the receiving end, fading parameters (α 1 , α 2 ) are estimated (α E1 , α E2 ) and the properties of complex conjugates are utilized ( 28, 29, 201, 202 ) to produce a result (r 1 , r 2 ) that is representative of the original block of bits.

BACKGROUND OF THE INVENTION

Present telecommunication system technology includes a wide variety ofwireless networking systems associated with both voice and datacommunications. An overview of several of these wireless networkingsystems is presented by Amitava Dutta-Roy, Communications Networks forHomes, IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roydiscusses several communication protocols in the 2.4 GHz band, includingIEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping(FHSS) protocols. A disadvantage of these protocols is the high overheadassociated with their implementation. A less complex wireless protocolknown as Shared Wireless Access Protocol (SWAP) also operates in the 2.4GHz band. This protocol has been developed by the HomeRF Working Groupand is supported by North American communications companies. The SWAPprotocol uses frequency-hopping spread spectrum technology to produce adata rate of 1 Mb/sec. Another less complex protocol is named Bluetoothafter a 10th century Scandinavian king who united several Danishkingdoms. This protocol also operates in the 2.4 GHz band andadvantageously offers short-range wireless communication betweenBluetooth devices without the need for a central network.

The Bluetooth protocol provides a 1 Mb/sec data rate with low energyconsumption for battery powered devices operating in the 2.4 GHz ISM(industrial, scientific, medical) band. The current Bluetooth protocolprovides a 10-meter range and a maximum asymmetric data transfer rate of723 kb/sec. The protocol supports a maximum of three voice channels forsynchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetoothprotocol treats all radios as peer units except for a unique 48-bitaddress. At the start of any connection, the initiating unit is atemporary master. This temporary assignment, however, may change afterinitial communications are established. Each master may have activeconnections of up to seven slaves. Such a connection between a masterand one or more slaves forms a “piconet.” Link management allowscommunication between piconets, thereby forming “scattemets.” TypicalBluetooth master devices include cordless phone base stations, localarea network (LAN) access points, laptop computers, or bridges to othernetworks. Bluetooth slave devices may include cordless handsets, cellphones, headsets, personal digital assistants, digital cameras, orcomputer peripherals such as printers, scanners, fax machines and otherdevices.

The Bluetooth protocol uses time-division duplex (TDD) to supportbi-directional communication. Frequency hopping permits operation innoisy environments and permits multiple piconets to exist in closeproximity. The frequency hopping scheme permits up to 1600 hops persecond over 79 1-MHZ channels or the entire 2.4 GHz ISM spectrum.Various error correcting schemes permit data packet protection by ⅓ and⅔ rate forward error correction. Further, Bluetooth uses retransmissionof packets for guaranteed reliability. These schemes help correct dataerrors, but at the expense of throughput.

The Bluetooth protocol is specified in detail in Specification of theBluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporatedherein by reference.

In wireless communication systems such as described above, thewell-known disadvantageous phenomenon of fading is encountered.Conventional transmit diversity techniques can provide several dB's ofgain to thereby at least partially overcome the fading problem. Someknown transmit diversity schemes require an estimate of the channel atthe transmitter, which estimate can be made from previous receptions atthe same frequency. However, because the operating environment is nottotally static, such estimates are sometimes not very accurate.

Another known technique for overcoming fading is antenna space timetransmit diversity. An example of this technique is disclosed in U.S.Ser. No. 09/205,029 (Attorney Docket No. TI-28441), filed on Dec. 3,1998 and incorporated herein by reference. The space time transmitdiversity disclosed therein is bit level space time transmit diversityfor use with linear modulation schemes such as QPSK modulation. However,bit level space time transmit diversity cannot be used in wirelesscommunication systems that utilize non-linear modulation schemes, forexample the GFSK modulation scheme utilized in Bluetooth systems.

It is therefore desirable to apply space time transmit diversitytechniques in wireless communication systems that utilize nonlinearmodulation.

The present invention applies space time transmit diversity to achievediversity gains in wireless communication systems that utilize nonlinearmodulation schemes. In particular, space time transmit diversity (STTD)is applied at the block level to an original block of bitsadvantageously to reduce the effects of fading in wireless communicationsystems that use nonlinear modulation schemes. At the receiving end,fading parameters are estimated and the properties of complex conjugatesare utilized to produce a result that is representative of the originalblock of bits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates pertinent portions of exemplaryembodiments of a transmitting station that implements block level spacetime transmit diversity according to the invention.

FIGS. 2-4 diagrammatically illustrate pertinent portions of exemplaryembodiments of a receiving station which implements block level spacetime transmit diversity according to the invention.

FIG. 5 diagrammatically illustrates pertinent portions of furtherexemplary embodiments of a transmitting station according to theinvention.

FIG. 6 illustrates exemplary operations which can be performed by thereceiving station of FIGS. 2-4.

FIG. 7 illustrates exemplary operations which can be performed by thetransmitting station of FIG. 1.

FIG. 8 illustrates exemplary operations which can be performed by thetransmitting station of FIG. 5.

FIG. 9 illustrates the communication performance of a nonlinearmodulation wireless communication system with (and without) block levelspace time transmit diversity according to the invention.

DETAILED DESCRIPTION

FIG. 1 diagrammatically illustrates pertinent portions of exemplaryembodiments of a transmitting station according to the invention. Forexample, the transmitting station of FIG. 1 could be a Bluetooth masteror slave device. In FIG. 1, input digital information bits are appliedto a block formatter 11 which establishes from the input bits anoriginal block of bits having two parts x₁ and x₂, shown generally at12. Parts x₁ and x₂ each include a plurality of bits. The two-part blockof bits 12 is input to a nonlinear modulator such as an FSK (or GFSK)modulator 13 which uses conventional techniques to modulate a carriersignal with the block of bits to produce at 14 a modulated block ofinformation including a first part a and a second part b whichrespectively correspond to the parts x₁ and X₂ at 12.

The two-part modulated block at 14 is input to an STTD encoder 15 whichoutputs at 9 a re-ordered two part block including a first part −b^(*)which represents the negative of the complex conjugate of the secondpart b of the modulated block at 14, and also including a second parta^(*) which is the complex conjugate of the first part a of themodulated block at 14. Complex conjugation as described herein can beperformed in any desired conventional manner. For example, if m= cos(w_(c)τ−φ(t)), then the complex conjugate m^(*)= cos (w_(c)τ−φ(t)). Asanother example, the part a^(*) of FIG. 1 can be produced by using thenegative of the bits that were used to produce the modulated part a inFIG. 1, that is, by also modulating −x₁ at 13. In such embodiments, themodulator 13 can provide both a^(*) and b^(*), as shown by broken linein FIG. 1 (i.e., the modulator 13 performs the complex conjugatefunction of the encoder 15), so the encoder at 15 need only perform there-ordering and negation operations.

The block output at 9 from the STTD encoder 15 is applied to a transmitprocessing section 17, and the modulated block 14 output from themodulator 13 is applied to another transmit processing section 19. Thetransmit processing sections 17 and 19 utilize conventional transmitprocessing techniques to effect transmission of the blocks 9 and 14across a wireless communication link 18 (e.g., a Bluetooth link) viarespective antennas 10 and 16. In the example of FIG. 1, transmission ofthe part a ^(*) of block 9 corresponds in time with transmission of thepart b of block 14, and transmission of the part −b^(*) of block 9corresponds in time with transmission of the part a of block 14, therebyproviding space and time transmit diversity. Also as shown in FIG. 1,the wireless communication channel associated with antenna 10 has afading parameter designated as α₁, and the wireless communicationchannel associated with antenna 16 has a fading parameter designated asα₂.

FIGS. 2 and 3 diagrammatically illustrate pertinent portions ofexemplary embodiments of a receiving station according to the invention.For example, the receiving station could be a Bluetooth master device ora Bluetooth slave device. As shown in FIG. 2, the wireless communicationsignals transmitted by antennas 10 and 16 of FIG. 1 are received at anantenna 20 of a wireless communication interface. The antenna 20 iscoupled to a receive processing section 21 of the wireless communicationinterface, which utilizes conventional receive processing techniques toproduce from the received antenna signals a block of informationincluding a first part c and a second part d, as designated generally at22. The block at 22 is input to a separator 23 which separates the blockinto its constituent parts c and d. Recalling from FIG. 1 that blocks 9and 14 were transmitted via the respective antennas 10 and 16 having therespective fading parameters α₁ and α₂ associated therewith, the parts cand d in FIG. 2 can be expressed as follows:c=α ₁ a−α ₂ b ^(*)  Equation 1d=α ₁ b+α ₂ a ^(*),  Equation 2

-   -   where the superscript “*” denotes the complex conjugate.

The receiving station can use conventional techniques to produceestimates α_(E1) and α_(E2) of the respective fading parameters α_(e1)and α_(e2). For example, a fading parameter estimater shown generally at200 can be a conventional linear receiver, which provides fadingparameter estimates in its normal operation. The fading parameterestimates α_(E1) and α_(E2) can be determined, for example, based onearlier transmissions received individually from the respective antennas10 and 16, and can be stored in a suitable database (not explicitlyshown). Using the estimated fading parameters, the following two signalscan be formed:r ₁=α_(E1) ^(*) c+α _(E2) d ^(*)  Equation 3r ₂=−α_(E2) c ^(*)+α_(*) ^(E1) d.  Equation 4

In FIG. 2, the multiplier pairs at 24 and 26, the adders at 25 and 27,and the complex conjugators at 201, 202, 28 and 29 form a combiner thatcombines the parts c and d with the estimates α_(E1) and α_(E2) toproduce the combined result signals r₁ and r₂ as defined by Equations 3and 4 above. Combining Equations 3 and 4 with Equations 1 and 2,utilizing the symmetry of complex conjugates, and assuming thatα_(E1)≈α₁, and α_(E2)≈α₂ the signals r₁ and r₂ can be expressed asfollows:r ₁=(|α_(E1)|²+|α_(E2)|²)a  Equation 5r ₂=(|α_(E1)|²+|α_(E2)|²)b  Equation 6

As illustrated in FIG. 3, the signals r₁ and r₂ are input to a blockformatter 31 which formats the signals r₁ and r₂ into a block ofinformation at 32 having a first part r₁ and a second part r₂. Thistwo-part block at 32 is input to a nonlinear (such as an FSK or GFSK)demodulator 33 which uses conventional demodulation techniques toproduce at 34 the receiving station's determination of the originalblock of bits (see also 12 in FIG. 1).

FIG. 4 diagrammatically illustrates further exemplary embodiments of areceiving station according to the invention. In the embodiment of FIG.4, the signals r₁ and r₂ from FIG. 2 are input to respective parallelnonlinear demodulators 41 which use conventional demodulation techniquesto produce the receiving station's determination of the first and secondparts x₁ and X₂ of the original block of bits (see also 12 in FIG. 1).

FIG. 5 diagrammatically illustrates pertinent portions of furtherexemplary embodiments of a transmitting station according to theinvention, which can be used in conjunction with the receiving stationof FIG. 4. In the embodiment of FIG. 5, the input bits are applied to aseparator 51 which produces therefrom the first and second parts x₁ andx₂ (see 12 in FIG. 1) in parallel format, thus providing the originalblock of bits in parallel format. The parts x₁ and x₂ are applied torespective parallel nonlinear modulators 54, which utilize conventionalmodulation techniques to produce a modulated block in parallel format,including the parts a and b which respectively correspond to the partsx₁ and x₂ (see also FIG. 1). The parts a and b are input to a blockformatter 55, which produces at 56 a block of information including theparts a and b, which block can then be input to the STTD encoder 15 andthe transmit processing section 19 of FIG. 1. Thus, the embodiment ofFIG. 5 provides an alternative arrangement for producing the two-partmodulated block illustrated generally at 14 in FIG. 1.

FIG. 6 illustrates exemplary operations which can be performed by thereceiving stations of FIGS. 2-4. After a block of information isreceived at 61, the block is divided (separated) into two parts at 62,and the signals r₁ and r₂ are formed at 63. Thereafter, the signals r₁and r₂ are demodulated (and downscaled) at 64 to produce the receivingstation's determination of the original block of bits.

FIG. 7 illustrates exemplary operations which can be performed by thetransmitting station of FIG. 1. At 71, a two-part block of bits isestablished (see 12 in FIG. 1). At 72, the two-part block of bits ismodulated to produce a two-part original modulated block (see 14 in FIG.1). At 73, the two parts of the original modulated block are re-orderedand complex-conjugated, and at 74 one of the re-ordered,complex-conjugated parts is negated, thereby producing an STTD block(see also 9 in FIG. 1). At 75, the original modulated block and the STTDblock are transmitted (in the timewise relationship described above)using respective first and second antennas.

FIG. 8 illustrates exemplary operations which can be performed by thetransmitting station of FIG. 5. At 81, the input bits are separated intotwo parts (original block in parallel format). At 82, the two parts arerespectively modulated to produce two corresponding modulated parts(modulated block in parallel format). At 83, the modulated parts areformatted into a two-part modulated block. From this point, operationscan proceed to 73 in FIG. 7 (see broken line in FIG. 7) and, after theoperations at 75 in FIG. 7, operations can return to 81 (see broken linein FIG. 7).

FIG. 9 illustrates exemplary simulation results for a conventionalnonlinear-modulated wireless communication system at 92 and for anonlinear-modulated wireless communication system which utilizes spacetime transmit diversity according to the invention at 94. The curve 94demonstrates better performance.

It will be evident to workers in the art that the embodiments of FIGS.1-8 can be readily implemented, for example, by suitably modifyingsoftware, hardware, or a combination of software and hardware, inconventional wireless transmitting and receiving stations that supportplural transmit antennas, for example Bluetooth master and slavedevices.

Although exemplary embodiments of the invention are described above indetail, this does not limit the scope of the invention, which can bepracticed in a variety of embodiments.

1. An antenna space time transmit diversity method, comprising:providing an original block of bits having first and second parts;modulating the original block of bits with a carrier signal to produce amodulated block of information having first and second parts thatrespectively correspond to said first and second parts of said originalblock of bits; producing a further block of information including firstand second parts which respectively correspond to the first and secondparts of the modulated block and which are respective complex conjugatesof the first and second parts of the modulated block; and using firstand second antennas to respectively transmit the modulated block and thefurther block over a wireless communication link such that the firstpart of the modulated block is transmitted in timewise correspondencewith the second part of the further block and the second part of themodulated block is transmitted in timewise correspondence with the firstpart of the further block.
 2. The method of claim 1, wherein one of theparts of the further block is a negative complex conjugate of thecorresponding part of the modulated block.
 3. The method of claim 1,wherein said providing step includes providing the first and secondparts of the original block in parallel, and wherein said modulatingstep includes modulating the first and second parts of the originalblock in parallel.
 4. The method of claim 1, wherein said demodulatingstep includes one of FSK and GFSK demodulating.
 5. A method ofdetermining an original block of bits from first and second antennasignals received via a wireless communication link, comprising:producing a received block of information from the first and secondantenna signals; complex conjugating first and second parts of thereceived block to produce first and second complex conjugate parts; andcombining the first and second parts and the first and second complexconjugate parts and fading parameter information indicative of first andsecond estimated fading parameters respectively associated with thefirst and second antenna signals to produce a combined result that isrepresentative of the original block of bits.
 6. The method of claim 5,wherein the fading parameter information includes a complex conjugate ofthe first estimated fading parameter and also includes the secondestimated fading parameter.
 7. The method of claim 5, wherein saidcombining step includes multiplying the first and second parts by acomplex conjugate of the first estimated fading parameter to producefirst and second products, respectively, and multiplying the first andsecond complex conjugate parts by the second estimated fading parameterto produce third and fourth products, respectively.
 8. The method ofclaim 7, wherein said combining step includes adding the first productto the third product to produce a first received part, and subtractingthe fourth product from the second product to produce a second receivedpart, said combined result including the first and second receivedparts.
 9. The method of claim 8, including demodulating the first andsecond received parts to produce a demodulated result, and making adetermination that the demodulated result is the original block of bits.10. The method of claim 9, wherein said demodulating step includesdemodulating the first and second received parts in parallel to producefirst and second constituent parts of the demodulated result.
 11. Themethod of claim 9, including formatting the first and second receivedparts into a further block, said demodulating step includingdemodulating the further block to produce a demodulated block, saidmaking step including making a determination that the demodulated blockis the original block of bits.
 12. The method of claim 9, wherein saiddemodulating step includes FSK demodulating.
 13. The method of claim 9,wherein said demodulating step includes GFSK demodulating.
 14. Anantenna space time transmit diversity apparatus, comprising: an inputfor receiving an original block of bits having first and second parts; amodulator coupled to said input for modulating the original block ofbits with a carrier signal to produce a modulated block of informationhaving first and second parts that respectively correspond to said firstand second parts of the original block of bits; an encoder coupled tosaid modulator for receiving the modulated block of information andproducing therefrom a further block of information including first andsecond parts which respectively correspond to the first and second partsof the modulated block and which are respective complex conjugates ofthe first and second parts of the modulated block; and first and secondantennas respectively coupled to said modulator and said encoder forrespectively transmitting the modulated block and the further block overa wireless communication link such that the first part of the modulatedblock is transmitted in timewise correspondence with the second part ofthe further block and the second part of the modulated block istransmitted in timewise correspondence with the first part of thefurther block.
 15. The apparatus of claim 14, wherein one of the partsof the further block is a negative complex conjugate of thecorresponding part of the modulated block.
 16. The apparatus of claim14, wherein said demodulator includes one of an FSK demodulator and aGFSK demodulator.
 17. The apparatus of claim 14, wherein a portion ofsaid encoder is provided in said demodulator.
 18. The apparatus of claim14, provided as a Bluetooth device.
 19. The apparatus of claim 14,wherein said modulator is operable for modulating the first and secondparts of the original block in parallel.
 20. A wireless communicationapparatus, comprising: a wireless communication interface for receivingfrom a wireless communication link first and second antenna signals thatrepresent an original block of bits, said wireless communicationinterface operable for producing a received block of information fromsaid first and second antenna signals; a complex conjugator coupled tosaid wireless communication interface for complex conjugating first andsecond parts of the received block to produce first and second complexconjugate parts; and a combiner coupled to said complex conjugator andto said wireless communication interface and having an input forreceiving fading parameter information indicative of first and secondestimated fading parameters respectively associated with the first andsecond antenna signals, said combiner operable for combining the firstand second parts and the first and second complex conjugate parts andthe fading parameter information to produce a combined result that isrepresentative of the original block of bits.
 21. The apparatus of claim20, wherein the fading parameter information includes a complexconjugate of the first estimated fading parameter and also includes thesecond estimated fading parameter.
 22. The apparatus of claim 20,wherein said combiner includes multipliers for multiplying the first andsecond parts by a complex conjugate of the first estimated fadingparameter to produce respective first and second products and formultiplying the first and second complex conjugate parts by the secondestimated fading parameter to produce respective third and fourthproducts.
 23. The apparatus of claim 22, wherein said combiner includesadders coupled to said multipliers for adding the first product to thethird product to produce a first received part and for subtracting thefourth product from the second product to produce a second receivedpart, said combined result including the first and second receivedparts.
 24. The apparatus of claim 23, including a demodulator coupled tosaid adders for demodulating the first and second received parts toproduce a demodulated result and for providing the demodulated result asa determination of the original block of bits.
 25. The apparatus ofclaim 24, wherein said demodulator is operable for demodulating thefirst and second received parts in parallel to produce first and secondconstituent parts of the demodulated result.
 26. The apparatus of claim24, including a formatter coupled between said demodulator and saidadders for formatting the first and second received parts into a furtherblock, said demodulator operable for demodulating the further block toproduce a demodulated block and for providing the demodulated block as adetermination of the original block of bits.
 27. The apparatus of claim20, wherein said demodulator includes one of an FSK demodulator and aGFSK demodulator.
 28. The apparatus of claim 20, provided as a Bluetoothdevice.